Add file attachment model and types

app/MindWork AI Studio/Chat/FileAttachment.cs

@@ -0,0 +1,6 @@
+namespace AIStudio.Chat;
+
+/// <summary>
+/// Represents an immutable file attachment with details about its type, name, path, and size.
+/// </summary>
+public readonly record struct FileAttachment(FileAttachmentType Type, string FileName, string FilePath, long FileSize);

app/MindWork AI Studio/Chat/FileAttachmentType.cs

@@ -0,0 +1,22 @@
+namespace AIStudio.Chat;
+
+/// <summary>
+/// Represents different types of file attachments.
+/// </summary>
+public enum FileAttachmentType
+{
+    /// <summary>
+    /// Document file types, such as .pdf, .docx, .txt, etc.
+    /// </summary>
+    DOCUMENT,
+    
+    /// <summary>
+    /// All image file types, such as .jpg, .png, .gif, etc.
+    /// </summary>
+    IMAGE,
+    
+    /// <summary>
+    /// All audio file types, such as .mp3, .wav, .aac, etc.
+    /// </summary>
+    AUDIO,
+}